This limited competition renewal application is for the Turku/Finland Clinical Center of The Environmental Determinants of Diabates in the Young (TEDDY) study. The primary objective of this multi-center, multi- national epidemiological study is the identification of infectious agents, dietary factors, or other environmental exposures that are associated with increased risk of islet autoimmunity and type 1 diabates mellitus (T1D). Factors affecting specific phenotypic manifestations such as early age of onset or rate of progression, or which provide protection from the development of T1D will also be identified. TEDDY is an observational cohort study in which newborns who are less than 4.5 months of age and have high risk HLA genotypes and come from the general population, or carry HLA risk alleles and are first-degree relatives of patients affected with T1D will be enrolled. Six Clinical Centers in the United States and Europe will screen 361,588 newborns of which it is anticipated that 17,804 will be eligible for enrollment, with just over 7,800 followed. Recruitment started in September 2004 and will continue until December 31, 2009. Participants will be followed to the age of 15 years. Identification of such etiologically important factors will lead to a better understanding of disease pathogenesis and result in new strategies to prevent, delay or reverse T1D.